phone number formatting

I'm working on a database file that has both foreign and domestic phone numbers in it. I need to add a "+" sign in front of all the numbers, what is the easiest way to go about this? Something is off in the formatting because when ever I try to do a custom format it doesn't change anything, nor does it change when I convert the format to a number. I am pretty sure all spaces have been removed but I cannot be certain. I've attached a copy for you to look at.

Thank you,

Dustin